Microcapsule, sheet material, circuit board, method for manufacturing circuit board, and computer readable storage medium

ABSTRACT

A microcapsule includes a shell including a conducting component, and a thermally expandable component contained in the shell and having a property of expanding by heating. The shell is deformable in accordance with expansion of the thermally expandable component when the thermally expandable component is heated.

CROSS-REFERENCE TO RELATED APPLICATION

This is a Continuation Application of U.S. application Ser. No.16/508,364 filed on Jul. 11, 2019, which is incorporated herein byreference.

BACKGROUND 1. Field

The present invention relates to microcapsules, sheet materials, circuitboards, methods for manufacturing a circuit board, and computer readablestorage media.

2. Related Art

According to a conventional method of creating a conductive circuit,e.g., a flexible wiring board described in JP 2000-223795 A, an operatorat the field firstly creates an electronic circuit diagram (see FIG.10A, for example) with a CAD (Computer-Aided Design) system. Next, theoperator prepares a base material and fabricates a flexible wiring board(see FIG. 10B, for example) by machining the base material with aspecialized machine. FIG. 10A shows one example of an electronic circuitdiagram 100 created with a CAD system. FIG. 10B shows one example of aflexible wiring board 300.

To create a circuit with a universal board (see FIG. 10C, for example)described in JP 2001-42763 A, for example, an operator manually connectssolder with the board. FIG. 10C shows an example of a universal board400.

Such a field of creating a conductive circuit needs a circuit boardhaving the wiring function equivalent to a flexible wiring board and auniversal board, and that can be created easily in a short time and atlow cost.

The afore-mentioned flexible wiring board described in JP 2000-223795 A,for example, is manufactured by creating an electronic circuit diagramwith a CAD (Computer-Aided Design) system, and then preparing a basematerial and fabricating a flexible wiring board by machining the basematerial with a specialized machine. The creation of such a flexiblewiring board therefore is limited to experts having an advancedknowledge of the field and requires certain time for creation. Thecreation of such a flexible wiring board also needs the cost, includingthe material cost and the facility cost. It is therefore difficult toprepare a plurality of types of flexible wiring boards. If thevalidation result of the created flexible wiring board shows anunfavorable operation, the operator is required to repeat the same job,which also needs a lot of cost and time for creation.

To create a circuit with the afore-mentioned universal board describedin JP 2001-42763 A, for example, an operator manually connects solderwith the board. Such creation of a circuit with a universal boardtherefore is a burden for the operator and requires certain time forpreparation. If the validation result of the created circuit shows anunfavorable operation, the operator is required to create anothercircuit again, which also requires a lot of cost and time for creation.

The present invention aims to provide a circuit board having the wiringfunction equivalent to a flexible wiring board and a universal board,and that can be prepared easily in a short time and at low cost.

SUMMARY

A microcapsule includes a shell includes a conducting component; and athermally expandable component contained in the shell and having aproperty of expanding by heating, the shell deforming due to expansionof the thermally expandable component to come in contact with anothercapsule and have a conducting state with the other capsule.

A thermally expandable material includes microcapsules and a binderhaving an insulating property, each microcapsule including a shellincluding a conducting component, and a thermally expandable componentcontained in the shell and having a property of expanding by heating,the shell deforming due to expansion of the thermally expandablecomponent to come in contact with another capsule and have a conductingstate with the other capsule.

A sheet material includes: a base layer; and a thermally expandablelayer disposed on the base layer, the thermally expandable layerincluding microcapsules and a binder having an insulating property, eachmicrocapsule including a shell including a conducting component, and athermally expandable component contained in the shell and having aproperty of expanding by heating, the shell deforming due to expansionof the thermally expandable component to come in contact with anothercapsule and have continuity with the other capsule.

A circuit board includes: a base layer; and a thermally expandable layerdisposed on the base layer, the thermally expandable layer having anot-expanding region and an expanding region, the not-expanding regiondefining an insulating region of a circuit, the expanding regiondefining a conducting region of the circuit, the thermally expandablelayer including microcapsules and a binder having an insulatingproperty, each microcapsule including a shell including a conductingcomponent, and a thermally expandable component contained in the shelland having a property of expanding by heating, the shell at theexpanding region deforming due to expansion of the thermally expandablecomponent to come in contact with another capsule and have continuitywith the other capsule.

A method for manufacturing a circuit board, includes: a first step ofpreparing a sheet material including a base layer and a thermallyexpandable layer disposed on the base layer; and a second step ofexpanding the sheet material partially so that a not-expanding region ofthe thermally expandable layer defines an insulating region of a circuitand an expanding region of the thermally expandable layer defines aconducting region of the circuit, the thermally expandable layerincluding microcapsules and a binder having an insulating property, eachmicrocapsule including a shell including a conducting component, and athermally expandable component contained in the shell and having aproperty of expanding by heating, the shell at the expanding regiondeforming due to expansion of the thermally expandable component to comein contact with another capsule and have continuity with the othercapsule.

A computer readable storage medium having stored thereon a program thatis executable by a computer, the program making the computer implementthe following functions to control a device to create a conversiondiagram: setting a resistance value of a resistance in an electroniccircuit diagram data; forming an image of at least a part of wiringincluded in the electronic circuit diagram data with photothermal ink;and expanding a thermally expandable layer in a sheet material to makeup a circuit board of an electronic circuit to be formed based on theelectronic circuit diagram data due to heat from the photothermal ink.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows the configuration of a sheet material according to oneembodiment.

FIG. 1B shows the structure of a thermally expandable layer of a sheetmaterial according to one embodiment.

FIG. 1C schematically shows the configuration of a microcapsuleaccording to one embodiment.

FIG. 2A is drawing (1) that shows a microcapsule according to oneembodiment.

FIG. 2B is drawing (2) that shows a microcapsule according to oneembodiment.

FIG. 2C is drawing (3) that shows a microcapsule according to oneembodiment.

FIG. 3A is drawing (1) that shows a formation step of a circuit board.

FIG. 3B is drawing (2) that shows a formation step of a circuit board.

FIG. 3C is drawing (3) that shows a formation step of a circuit board.

FIG. 3D is drawing (4) that shows a formation step of a circuit board.

FIG. 4A shows a region of the thermally expandable layer to be expandedand shows the state before expansion.

FIG. 4B shows the region of the thermally expandable layer to beexpanded and shows the state during expansion.

FIG. 4C shows the region of the thermally expandable layer to beexpanded and shows the state after expansion.

FIG. 5A shows one example of a conversion-diagram creation device.

FIG. 5B shows an example of an input screen.

FIG. 6A is drawing (1) that shows a modified example of a conversiondiagram.

FIG. 6B is drawing (2) that shows a modified example of a conversiondiagram.

FIG. 6C is drawing (3) that shows a modified example of a conversiondiagram.

FIG. 6D is drawing (4) that shows a modified example of a conversiondiagram.

FIG. 6E is drawing (5) that shows a modified example of a conversiondiagram.

FIG. 7A is drawing (1) that shows a creation example of a circuit board.

FIG. 7B is drawing (2) that shows a creation example of a circuit board.

FIG. 7C is drawing (3) that shows a creation example of a circuit board.

FIG. 8 shows one example of a circuit board created by the presentembodiment.

FIG. 9A is drawing (1) that shows a button structure.

FIG. 9B is drawing (2) that shows a button structure.

FIG. 10A shows an example of an electronic circuit diagram.

FIG. 10B shows one example of a flexible wiring board.

FIG. 10C shows one example of a universal board.

DETAILED DESCRIPTION

The following describes an embodiment of the present invention(hereinafter called a present embodiment) in details, with reference tothe drawings. The drawings are just schematic views to enable sufficientunderstanding of the present invention. The present invention thereforeis not limited to the examples shown in these drawings. Like numbersindicate like components throughout the drawings, and their duplicateddescriptions are omitted.

Embodiment

A circuit board 30 (see FIG. 8) of the present embodiment is createdwith a sheet material 40 (see FIG. 1A) described later. This sheetmaterial 40 includes a thermally expandable layer 42 (see FIG. 1A)described later. When heated, this thermally expandable layer 42partially expands to be a desired pattern. This expansion of thethermally expandable layer creates a circuit board 30 (see FIG. 8).

<Configuration of a Sheet Material to Create a Circuit Board>

Referring to FIG. 1A to FIG. 1C, the following describes theconfiguration of a sheet material 40 to create a circuit board 30 (seeFIG. 8). FIG. 1A shows the configuration of the sheet material 40. FIG.1B shows the configuration of a thermally expandable material used forthe thermally expandable layer 42 (see FIG. 1A) of the sheet material40. FIG. 1B is an enlarged view of region Ar of the thermally expandablelayer 42 in FIG. 1A. FIG. 1C schematically shows the configuration of amicrocapsule 51 included in the thermally expandable layer 42.

As shown in FIG. 1A, the sheet material 40 includes the thermallyexpandable layer 42 and a microfilm 44 on a base layer (base) 41.

The base layer (base) 41 includes paper or resin, such as PET(polyethylene terephthalate). The base layer 41 preferably has heatresistance. The base layer 41 preferably is flexible moderately.

The thermally expandable layer 42 expands by heating.

The microfilm 44 is a layer to print (apply) photothermal ink 45 (seeFIG. 3A).

As shown in FIG. 1B, the thermally expandable layer 42 includesthermally expandable ink 50 as a thermally expandable material. In oneexample, the thermally expandable layer 42 is formed by applying thethermally expandable ink 50 that is a thermally expandable material inthe liquid form on the base layer 41, followed by drying.

The thermally expandable ink 50 (thermally expandable material) includesmicrocapsules 51 having a conducting property that are mixed in a binder56 having an insulating property. Photothermal ink 45 is printed(applied) at a region of the microfilm 44 (see FIG. 3A) of the sheetmaterial 40. When such a sheet material 40 is irradiated with light, thethermally expandable layer 42 at a part corresponding to the printedregion expands.

The binder 56 includes emulsion of a resin material. Emulsion is asubstance including a dispersion medium and dispersed material, both ofwhich are in the liquid form.

Each microcapsule 51 includes a shell 52 and a core 53. The core 53 is athermally expandable component contained in the shell 52. FIG. 1B showsthe contained core 53 by cutting the shell 52 at an about quarter parton the front. In one example, the shell 52 includes acrylonitrilecopolymer as thermoplastic resin. The shell 52 includes a metal filler57 as a conductive component, and so has a conducting property. The core53 contained in the shell 52 includes hydrocarbon 54, and has aninsulating property. The hydrocarbon 54 has a thermally expandableproperty that expands by heating.

“Thermoplasticity” of a material as stated above refers to a propertythat the material is plastically deformed when it is heated underpressure. “Thermal expandable property” of a material as stated aboverefers to a property that the material expands when it is heated.

Preferably the hydrocarbon 54 is in the liquid form and has a relativelylow boiling point (liquid low-boiling hydrocarbon). In one example, thehydrocarbon 54 includes the following components in the increasing orderof the number of carbons.

Methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), pentane(C₅H₁₂), hexane (C₆H₁₄), heptane (C₇H₁₆), octane (C₈H₁₈), nonane(C₉H₂₀), and decane (C₁₀H₂₂).

The boiling point of the hydrocarbon 54 increases with the number ofcarbons. In one example, the above-mentioned components have thefollowing boiling points.

The boiling points of methane, ethane, propane, butane, pentane, hexane,heptane, octane, nonane, and decane are −162° C., −89° C., −42° C., −1°C., 36.1° C., 68° C., 98.42° C., 125° C., 151° C., and 174.1° C.,respectively.

In the present embodiment, the hydrocarbon 54 includes a singlecomponent or two or more types of components in combination of thesecomponents so that the hydrocarbon expands at a desired temperature(expansion temperature).

As shown in FIG. 1C, the core 53 of each microcapsule 51 expands byheating. FIG. 1C shows the microcapsule 51 having a part cut on theupper right to explain the cross-sectional structure of the shell 52(the same applies to FIG. 2A to FIG. 2C). The shell 52 of themicrocapsule 51 deforms so as to extend with the expansion of the core53 (thermally expandable component). The shell 52 has a conductingproperty. When the shell 52 deforms due to the expansion of the core 53(thermally expandable component), the shell 52 comes in contact withanother capsule to form a conducting region between these capsules.

The microcapsule 51 includes a metal filler 57 as a conductive componentin the shell 52 (see FIG. 2A to FIG. 2C). FIG. 2A to FIG. 2C show theconfigurations of the microcapsule 51. The microcapsule 51 has any oneof the configurations shown in FIG. 2A to FIG. 2C.

In the example of FIG. 2A, the shell 52 of the microcapsule 51 includesa resin material having metal filler 57 mixed therein.

In the example of FIG. 2B, the shell 52 of the microcapsule 51 includesan outer layer 52 a including a resin material having the metal filler57 mixed therein, and an inner layer 52 b including a resin material nothaving the metal filler 57 mixed therein.

In the example of FIG. 2C, the shell 52 of the microcapsule 51 includesa resin material coated with the metal filler 57 on the surface.

<Formation Step of Circuit Board>

Referring to FIG. 3A to FIG. 3D, the following describes formation stepsof the circuit board 30. FIG. 3A to FIG. 3D show the formation steps ofthe circuit board 30, showing a change in the cross-sectional shape ofthe sheet material 40.

As shown in FIG. 3A, the overall region of the sheet material 40 is aninsulating region. The operator sets such a sheet material 40 at anot-illustrated printer of an ink-jet scheme. The operator then prints(applies) photothermal ink 45 at a region of the microfilm 44corresponding to the region of the thermally expandable layer 42 to beexpanded with the not-illustrated printer.

In the present embodiment, the “region of the thermally expandable layer42 to be expanded” means a conducting region, such as wiring andconnecting terminals, in the circuit board 30 (see FIG. 8). Thephotothermal ink 45 is black ink including carbon black. Thephotothermal ink 45 absorbs light and converts the absorbed light intoheat.

Next as shown in FIG. 3B, the operator disposes the sheet material 40with the printed photothermal ink 45 near a heater 103 (heat source),and applies light to the sheet material 40 from the heater 103.

In one example, the heater 103 (heat source) includes a halogen heater.When irradiated with light from the heater 103, the photothermal ink 45of the sheet material 40 converts the light into heat. Then thethermally expandable layer 42 located under the printed region of thephotothermal ink 45 reacts to the heat and partially expands. This formsan expanding region in the sheet material 40.

The expanding region of the sheet material 40 defines a conductingregion, and a not-expanding region of the sheet material 40 defines aninsulating region. The principle to change the layer structure in thisway is described later referring to FIG. 4A to FIG. 4C.

Next as shown in FIG. 3C, the operator peels off the microfilm 44 fromthe thermally expandable layer 42 for removal. In this way the operatorexposes the thermally expandable layer 42 as shown in FIG. 3D.

Using such a sheet material 40, the operator forms a circuit board 30having a conductive circuit of any pattern.

<Principle to Change the Layer Structure>

The thermally expandable layer 42 of the sheet material 40 changes inthe layer structure as shown in FIG. 4A, FIG. 4B and FIG. 4C, showingthe state before expansion, during expansion, and after expansion,respectively. FIG. 4A shows a region of the thermally expandable layer42 to be expanded and shows the state before expansion. FIG. 4B showsthe region of the thermally expandable layer 42 to be expanded and showsthe state during expansion. FIG. 4C shows the region of the thermallyexpandable layer 42 to be expanded and shows the state after expansion.

As shown in FIG. 4A, before expansion of the thermally expandable layer42, none of the microcapsules 51 mixed in the thermally expandable layer42 expand at the region of the thermally expandable layer 42 to beexpanded. Most of the microcapsules 51 therefore are not in contact withother capsules at their shells 52. In this state, a sufficient amount ofthe insulating binder 56 is present around most of the microcapsules 51.This means that the region of the thermally expandable layer 42 to beexpanded in this state defines an insulating region.

As shown in FIG. 4B, during expansion of the thermally expandable layer42, a very limited part of the microcapsules 51 mixed in the thermallyexpandable layer 42 expands at the region of the thermally expandablelayer 42 to be expanded. Although a part of the microcapsules 51 is incontact with other capsules at the shells 52, most of the microcapsules51 still are not in contact with other capsules at their shells 52. Inthis state, a sufficient amount of the insulating binder 56 is stillpresent around most of the microcapsules 51. This means that the regionof the thermally expandable layer 42 to be expanded in this state stilldefines an insulating region.

As shown in FIG. 4C, after expansion of the thermally expandable layer42, a part (or all) of the microcapsules 51 mixed in the thermallyexpandable layer 42 expands at the region of the thermally expandablelayer 42 to be expanded. Most of the microcapsules 51 therefore are incontact with other capsules at their shells 52. In this state, only asmall amount of the insulating binder 56 is present around themicrocapsules 51. The conducting shells 52 are in contact with othercapsules and so have continuity with the other capsules. This means thatthe expanding region of the thermally expandable layer 42 defines aconducting region. Preferably the expanding region of the thermallyexpandable layer 42 has elasticity.

<Creation of a Conversion Diagram>

The operator to create the circuit diagram 30 (see FIG. 8) prepares anelectronic circuit diagram data D10 (see FIG. 5B) for an electroniccircuit diagram 10 (see FIG. 5B) designed beforehand, for example. Theoperator may design an electronic circuit diagram 10 of various patterns(see FIG. 5B) depending on the operations. To create the circuit board30 (see FIG. 8), the operator uses a computer 101 of FIG. 5A, forexample, that functions as a conversion-diagram creation device. Thecomputer 101 creates a conversion diagram 20 (see FIG. 6A to FIG. 6E)corresponding to the electronic circuit diagram 10 (see FIG. 5B). Theconversion diagram 20 shows an image to be formed with the photothermalink 45. FIG. 5A shows one example of the conversion-diagram creationdevice.

The computer 101 as the conversion-diagram creation device includes aCPU 101 a, a memory unit 101 b, a display unit 101 c, and an input unit101 d. The memory unit 101 b has a control program Pr installedbeforehand to create the conversion diagram 20 from the electroniccircuit diagram 10. The computer 101 creates the conversion diagram 20from the electronic circuit diagram 10 in accordance with the controlprogram Pr.

As shown in FIG. 5B, for example, the operator selects resistance Ar1,Ar2, or Ar3 of the electronic circuit diagram 10 on the input screen IMdisplayed at the display unit 101 c and sets a resistance value for theselected resistance. In this way, the operator forms a resistancecircuit of a pattern in accordance with the resistance values ofresistances Ar1, Ar2 and Ar3. FIG. 5B shows one example of the inputscreen IM. In the example of FIG. 5B, the electronic circuit diagram 10of the electronic circuit diagram data D10 shows a circuit 11 includingresistances Ar1, Ar2 and Ar3 disposed between three connecting terminals13 a, 13 b, and 13 c.

Each resistance may have a predetermined resistance value by adjustingthe line width (thickness/area), the density, and the length of an imageof resistance wirings 12 formed with the photothermal ink 45 (see FIG.3A). The operator is allowed to replace any component with anothercomponent, delete any component or dispose a new component.

Referring to FIG. 6A to FIG. 6E, the following describes a conversionexample of the conversion diagram 20. FIG. 6A to FIG. 6E each show anexample of conversion of the conversion diagram 20. FIG. 6A to FIG. 6Deach show the shape of the resistance wiring 12 formed with thephotothermal ink 45 (see FIG. 3A). FIG. 6E shows the shape of theresistance wiring 12 formed with the photothermal ink 45 (see FIG. 3A)as well as the shape of a protective film 29 on the resistance wiring12. The protective film 29 is formed with color ink 28 (insulating ink)having an insulating property.

Assume the case where the operator sets a resistance value of theresistances Ar1, Ar2 and Ar3 of the electronic circuit diagram 10 at 10Ω on the input screen IM (see FIG. 5B). As shown in FIG. 6A, thecomputer 101 then automatically creates conversion diagram data D20 a ofthe conversion diagram 20 a corresponding to the configuration of theelectronic circuit diagram data D10 (see FIG. 5B) in accordance with theelectronic circuit diagram data D10. In the example of FIG. 6A, theconversion diagram 20 a of the conversion diagram data D20 a includesthe resistance wirings 12 that have relatively large line widths(thickness/area) so as to correspond to the resistance value 10 Ω of theresistances Ar1, Ar2 and Ar3.

Assume the case where the operator sets a resistance value of theresistances Ar1, Ar2 and Ar3 of the electronic circuit diagram 10 at 100Ω on the input screen IM (see FIG. 5B). As shown in FIG. 6B, thecomputer 101 then automatically creates conversion diagram data D20 b ofthe conversion diagram 20 b corresponding to the configuration of theelectronic circuit diagram data D10 (see FIG. 5B) in accordance with theelectronic circuit diagram data D10. In the example of FIG. 6B, theconversion diagram 20 b of the conversion diagram data D20 b includesthe resistance wirings 12 that have line widths (thickness) smaller thanthose of the conversion diagram data D20 a (see FIG. 6A) so as tocorrespond to the resistance value 100 Ω of the resistances Ar1, Ar2 andAr3.

Assume the case where the operator sets a resistance value of theresistances Ar1, Ar2 and Ar3 of the electronic circuit diagram 10 at1000 Ω on the input screen IM (see FIG. 5B). As shown in FIG. 6C, thecomputer 101 then automatically creates conversion diagram data D20 c ofthe conversion diagram 20 c corresponding to the configuration of theelectronic circuit diagram data D10 (see FIG. 5B) in accordance with theelectronic circuit diagram data D10. In the example of FIG. 6C, theconversion diagram 20 c of the conversion diagram data D20 c includesthe resistance wirings 12 that have line widths (thickness) and heights(density) that are smaller than those of the conversion diagram data D20b (see FIG. 6B) so as to correspond to the resistance value 1000 Ω ofthe resistances Ar1, Ar2 and Ar3. A smaller height (smaller density) ofan image of the resistance wiring 12 formed with the photothermal ink 45(see FIG. 3A) means a smaller height of the expansion of the thermallyexpandable layer 42.

Assume the case where the operator sets a resistance value of theresistances Ar1, Ar2 and Ar3 of the electronic circuit diagram 10 at10000 Ω on the input screen IM (see FIG. 5B). As shown in FIG. 6D, thecomputer 101 then automatically creates conversion diagram data D20 d ofthe conversion diagram 20 d corresponding to the configuration of theelectronic circuit diagram data D10 (see FIG. 5B) in accordance with theelectronic circuit diagram data D10. In the example of FIG. 6D, theconversion diagram 20 d of the conversion diagram data D20 d includesthe resistance wirings 12 that are longer than those of the conversiondiagram data D20 b (see FIG. 6B) so as to correspond to the resistancevalue 10000 Ω of the resistances Ar1, Ar2 and Ar3. The conversiondiagram data D20 d includes long resistance wirings 12 so as to increasethe resistance value of the resistance wirings 12.

In the examples shown in FIG. 6A to FIG. 6D, the circuit 11 includes theresistance wirings 12 as conductors that are exposed. Preferably thecircuit 11 is configured to avoid short-circuit at the resistancewirings 12 with metal, for example, that is placed on the resistancewirings 12. In one example as shown in FIG. 6E, the circuit 11preferably includes a protective film 29 on the resistance wirings 12,and the protective film 29 is formed with color ink 28 (insulating ink)having an insulating property. In one example, the operator designates adesired region of the electronic circuit diagram 10 as the region toform the protective film 29 on the input screen IM (see FIG. 5B). Asshown in FIG. 6E, the computer 101 then automatically determines theregion to form the protective film 29 and creates a conversion diagram20 e including such a region in accordance with the electronic circuitdiagram data D10 (see FIG. 5B), and creates conversion diagram data D20e indicating the conversion diagram 20 e. In one example, the protectivefilm 29 is formed by overlaying the color ink 28 printed with anot-illustrated printer. The protective film 29 functions as aninsulating layer so as to avoid short-circuit with metal, for example,that is placed on the resistance wirings 12. The example in FIG. 6Eshows the conversion diagram 20 e including the protective film 29formed over the entire region of the resistance wirings 12. In anotherexample, the computer 101 may create a conversion diagram 20 e includingthe protective film 29 formed over only a part of the resistance wirings12.

<Creation of Circuit Board>

Referring to FIG. 7A to FIG. 7C, the following describes creation of thecircuit board 30. FIG. 7A to FIG. 7C show examples of the circuit board30.

The example shown in FIG. 7A includes three connecting terminals 13 a,13 b, and 13 c on the surface of the sheet material 40.

The operator sets a sheet material 40 at a not-illustrated printer. Theoperator then prints (applies) photothermal ink 45 at a regioncorresponding to the region of the thermally expandable layer 42 to beexpanded (see FIG. 3A) with the not-illustrated printer as shown in FIG.7B.

Next the operator disposes the sheet material 40 near a heater 103 (seeFIG. 3B), and applies light to the sheet material 40 from the heater 103(see FIG. 3B). The photothermal ink 45 of the sheet material 40 convertsthe applied light into heat. This generates heat at the printed part(see FIG. 7B) of the photothermal ink 45. As a result, the thermallyexpandable layer 42 (see FIG. 3B) of the sheet material 40 partiallyexpands to define three-dimensional resistance wirings 12 on the sheetmaterial 40 as shown in FIG. 7C. After that, the operator peels off themicrofilm 44 from the thermally expandable layer 42 (see FIG. 3C) toexpose the thermally expandable layer 42 (see FIG. 3D). This creates thecircuit board 30.

Such a circuit board 30 includes a desired region, including theresistance wirings 12 and connecting terminals not illustrated, that areexpanded to form conducting regions, so as to configure an operatingcircuit. The circuit board 30 has a wiring function equivalent to aflexible wiring board and a universal board, for example.

The operator uses such a sheet material 40 having a circuit 11 formedthereon as the circuit board 30. The operator may separate any part fromthe sheet material 40 to create a various shaped circuit board 30. Inthe example shown in FIG. 8, a circuit 11 is formed on the sheetmaterial 40. FIG. 8 shows one example of the circuit board 30 created bythe present embodiment. The operator separates a part of the circuit 11from the sheet material 40 shown in FIG. 8 to create a circuit board 30.

<Major Features of Sheet Material and Circuit Board>

The sheet material 40 of the present embodiment includes the base layer41, and the thermally expandable layer 42 formed on the base layer 41.The thermally expandable layer 42 includes the microcapsules 51 and thebinder 56 having an insulating property. Each microcapsule 51 includes ashell 52 containing a conducting component (metal filler 57), and athermally expandable component (core 53) contained in the shell 52 andhaving a property of expanding by heating. The shell 52 deforms due tothe expansion of the thermally expandable component (core 53) and socomes in contact with another capsule to have continuity with the othercapsule.

The circuit board 30 of the present embodiment is formed by partiallyexpansion of such a sheet material 40. In the circuit board 30 of thepresent embodiment, a not-expanding region of the thermally expandablelayer 42 defines an insulating region of the circuit 11. The expandingregion of the thermally expandable layer 42 defines a conducting regionof the circuit 11. Such a circuit board 30 has a wiring functionequivalent to a flexible wiring board and a universal board.

The circuit board 30 is created simply by printing a desired patterncorresponding to the conversion diagram 20 on the sheet material 40 withthe photothermal ink 45, and partially expanding the sheet material 40.Such a circuit board 30 is manufactured using low-cost materials, and sois manufactured at low cost. Such a circuit board 30 is created easilyin short time.

Such a circuit board 30 is created by facility that is a general-purposedevice (e.g., the computer 101 (see FIG. 5A), a printer (notillustrated), and the heater 103 (see FIG. 3B)) and is not a specializeddevice. The manufacturing cost of a circuit board 30 therefore reduces.

Such a circuit board 30 is created without jobs, such as soldering. Thecircuit board 30 can reduce burden on the operator to create the circuitboard. A large amount of such a circuit board 30 is manufactured inshort time.

Since the circuit board 30 is at low cost, the operator may create aplurality of types of circuit board 30 in small amounts, for example.The operator therefore may create a plurality of types of circuit boards30 as prototypes of a circuit used for the product being developed, forexample, and may conduct various tests with these created circuit boards30.

The circuit board 30 may have a different resistance value in accordancewith the expansion height of the expanding region of the thermallyexpandable layer 42. In other words, the operator may know a change inthe resistance value of the circuit board 30 in accordance with theexpansion height of the expansion region. For instance, when theoperator touches the expanding region of such a circuit board 30 withtheir hand, then the operator may know a change in the resistance valuefrom the tactile sensing with the hand. In other words, the circuitboard 30 allows the operator to know a change in the resistance valuebased on the tactile sensing with the hand in addition to the visualsense.

After the circuit 11 is formed on the circuit board 30, the photothermalink 45 may be printed and be partially expanded again. This changes theoriginal circuit 11 to another circuit or changes the original circuit11 so as to hide the configuration of the circuit (i.e., to embed theoriginal circuit 11 for deletion in the new expanding region). Thisallows the operator to conduct various tests of the created circuit 11on the circuit board 30 before factory shipment, to change the originalcircuit 11 to another circuit, or to change the original circuit 11 soas to hide the configuration of the original circuit 11 for the factoryshipment, for example. Such a circuit board 30 improves theconfidentiality of the circuit 11.

The circuit board 30 has a high level of safety because it mainlyinclude paper or resin, such as PET. The circuit board 30 therefore maybe used for teaching materials of science, teaching materials in scienceclasses, and materials for handicraft for kids, for example.

As stated above, the sheet material 40 of the present embodimentprovides a circuit board 30 having the wiring function equivalent to aflexible wiring board and a universal board, and that can be preparedeasily in a short time and at low cost.

The present invention is not limited to the above embodiment, and may bechanged or modified variously without departing from the scope of theinvention.

For instance, the embodiment as stated above shows the details forillustrative purpose of the gist of the present invention. The presentinvention therefore is not limited to the example including all of theelements described above. The present invention may include anothercomponent added to a certain component of the components as statedabove, or may include other components instead of some components of thecomponents as stated above. A part of the components as stated above ofthe present invention may be omitted.

In one example, a button structure 80 shown in FIG. 9A may be createdusing the sheet material 40 of FIG. 1A. FIG. 9A shows the buttonstructure 80 including the sheet material 40.

As shown in FIG. 9A, the button structure 80 has insulating regions 48 aand 48 b, and a conducting region 49 surrounded with the insulatingregions 48 a and 48 b. As shown in FIG. 1B, the conducting region 49includes a thermally expandable layer 42 including expandingmicrocapsule 51 each having a shell 52 having a conducting property anda thermally expandable component (core 53) contained in the shell 52.The conducting region 49 functions as a variable resistance that variesin resistance value when being pressed as indicated with the hollowarrow. Such a button structure 80 may include terminals at theconducting region 49 to apply voltage. Pressing or not of such a buttonstructure 80 may be detected based on a change of the voltage (orcurrent) applied to the terminals.

In another example, a button structure 80A may be created as shown inFIG. 9B, which includes a sheet material 40A that is a modified exampleof the sheet material 40. FIG. 9B shows the button structure 80Aincluding the sheet material 40A that is a modified example of the sheetmaterial 40.

As shown in FIG. 9B, the sheet material 40A includes the laminate on thebase layer 41, the laminate including a first conducting layer 49 a, athermally expandable layer 42 and a second conducting layer 49 b. Thebutton structure 80A includes such a sheet material 40A. In this buttonstructure 80A, the thermally expandable layer 42 expands partially. Suchan expanding region of the thermally expandable layer 42 has a heightthat keeps an insulating property. That is, the expanding region of thethermally expandable layer 42 is in the state during expansion as shownin FIG. 4B, for example. This means that the expanding region of thethermally expandable layer 42 defines an insulating region when thebutton structure is not pressed, i.e., the thermally expandable layer 42is an insulating layer 48.

Such a button structure 80A includes the laminate of the firstconducting layer 49 a, the insulating layer 48, and the secondconducting layer 49 b. The insulating layer 48 includes the thermallyexpandable layer 42 including expanding microcapsule 51 each having ashell 52 having a conducting property and a thermally expandablecomponent (core 53) contained in the shell 52. When being pressed asindicated with the hollow arrow, the conducting shell 52 of eachmicrocapsule 51 in the thermally expandable layer 42 comes in contactwith another capsule to have continuity with the other capsule as shownin FIG. 4C, for example. That is, the insulating layer 48 of the buttonstructure 80A functions as a variable resistance that varies inresistance value when being pressed as indicated with the hollow arrow.Such a button structure 80A may include terminals at the firstconducting layer 49 a and the second conducting layer 49 b to applyvoltage, for example. Pressing or not of such a button structure 80A maybe detected based on a change of the voltage (or current) applied to theterminals.

What is claimed is:
 1. A circuit board comprising: a base layer; and athermally expandable layer disposed on the base layer, the thermallyexpandable layer having a not-expanding region and an expanding region,the not-expanding region defining an insulating region of a circuit, theexpanding region defining a conducting region of the circuit, and thethermally expandable layer including a plurality of microcapsules and abinder having an insulating property, wherein: each of the plurality ofmicrocapsules includes (i) a shell including a conducting component and(ii) a thermally expandable component contained in the shell and havinga property of expanding by heating, and the shell of a firstmicrocapsule in the expanding region, from among the plurality ofmicrocapsules, is deformable in accordance with expansion of thethermally expandable component of the first microcapsule by heating soas to come into contact with the shell of a second microcapsule of theplurality of microcapsules.
 2. A sheet material comprising: a baselayer; and a thermally expandable layer disposed on the base layer, thethermally expandable layer including a plurality of microcapsules and abinder having an insulating property, wherein: each of the plurality ofmicrocapsules includes (i) a shell including a conducting component and(ii) a thermally expandable component contained in the shell and havinga property of expanding by heating, and the shell of a firstmicrocapsule of the plurality of microcapsules is deformable inaccordance with expansion of the thermally expandable component of thefirst microcapsule by heating so as to come into contact with the shellof a second microcapsule of the plurality of microcapsules.
 3. A methodfor manufacturing a circuit board, the method comprising: preparing asheet material including a base layer and a thermally expandable layerdisposed on the base layer; and partially expanding the sheet materialso that a not-expanding region of the thermally expandable layer definesan insulating region of a circuit and an expanding region of thethermally expandable layer defines a conducting region of the circuit,wherein: the thermally expandable layer includes a plurality ofmicrocapsules and a binder having an insulating property, each of theplurality of microcapsules includes (i) a shell including a conductingcomponent and (ii) a thermally expandable component contained in theshell and having a property of expanding by heating, and in thepartially expanding the sheet material, the shell of a firstmicrocapsule in the expanding region, from among the plurality ofmicrocapsules, deforms in accordance with expansion of the thermallyexpandable component by heating so as to come into contact with theshell of a second microcapsule of the plurality of microcapsules.
 4. Themethod for manufacturing the circuit board according to claim 3, whereinat least one of a thickness and an area of the expanding region is setin accordance with a set resistance value.
 5. The method formanufacturing the circuit board according to claim 4, wherein: theresistance value increases with an increase in the at least one of thethickness and the area of the expanding region, and the resistance valuedecreases with a decrease in the at least one of the thickness and thearea of the expanding region.
 6. The method for manufacturing thecircuit board according to claim 3, wherein a length of the expandingregion is set in accordance with a set resistance value.
 7. The methodfor manufacturing the circuit board according to claim 6, wherein: theresistance value increases with an increase in the length of theexpanding region, and the resistance value decreases with a decrease inthe length of the expanding region.
 8. A non-transitory computerreadable storage medium having stored thereon a program that isexecutable by a computer to cause the computer to implement functionsfor forming a circuit board of an electronic circuit, the functionscomprising: setting a resistance value of a resistance included inelectronic circuit diagram data of the electronic circuit; after thesetting the resistance value, converting the electronic circuit diagramdata to a conversion diagram used to form an image of at least a part ofwiring included in the electronic circuit diagram data; and forming theimage with photothermal ink on a thermally expandable layer included ina sheet material, based on the conversion diagram, wherein the circuitboard is formed by expanding areas of the thermally expandable layer onwhich the image has been formed by heat generated by the photothermalink.
 9. The non-transitory computer readable storage medium according toclaim 8, wherein a thickness of a line in the conversion diagram isdetermined in accordance with a resistance value of a wiring in theelectronic circuit diagram data corresponding to the line.
 10. Thenon-transitory computer readable storage medium according to claim 9,wherein: the resistance value increases with an increase in thethickness of the line, and the resistance value decreases with adecrease in the thickness of the line.
 11. The non-transitory computerreadable storage medium according to claim 8, wherein a length of a linein the conversion diagram is determined in accordance with a resistancevalue of a wiring in the electronic circuit diagram data correspondingto the line.
 12. The non-transitory computer readable storage mediumaccording to claim 11, wherein: the resistance value increases with anincrease in the length of the line, and the resistance value decreaseswith a decrease in the length of the line.
 13. The non-transitorycomputer readable storage medium according to claim 8, wherein a densityof a line in the conversion diagram is determined in accordance with aresistance value of a wiring in the electronic circuit diagram datacorresponding to the line.
 14. The non-transitory computer readablestorage medium according to claim 13, wherein: the resistance valueincreases with an increase in the density of the line, and theresistance value decreases with a decrease in the density of the line.15. The non-transitory computer readable storage medium according toclaim 8, the functions further comprising: forming a protective filmwith insulating ink having an insulating property, a region in which theprotective film is formed being determined based on the electroniccircuit diagram data.